Ross Martin read a script when it was first given to him, then did a pen-and-ink drawing of the character he was going to play, down to the last detail, glasses, mustache, clothes, posture, shoes, et cetera. Then, he brought the sketch to Make-up Artist Don Schoenfeld, and together they molded his face until it looked like the drawing.
The recurring science fiction theme, where genius scientists in the 1870s invent technology which didn't exist in the real world until several decades later, has come to be called "steampunk", a term coined in the 1980s.
During the fourth season, Ross Martin had a heart attack and missed several episodes. In production order, Martin did not appear in episodes 93-101, a total of nine. Charles Aidman appeared in four episodes (93-96). William Schallert in two (97-98). Alan Hale, Jr. in #99, John Williams in #100, and Steve Carlson in #101. Martin returned in episode #102, "The Night of the Diva", but there were only two more episodes shot after that.
All the action that took place inside the train was shot on a set in the studio. The "car" had removable walls so that the camera could maneuver. This is especially obvious when someone is coming in or going out since there is always a bush visible outside which blocked the interior of the soundstage. Even when the long shot shows a desert with nothing around the car, the bush is still seen.
Robert Conrad has stated that the very tight pants he wore on the show often split open during action scenes. This is especially obvious in several wide angle shots of fight scenes in which Conrad's period incorrect Jockey shorts are clearly visible.
James and Artemus had two different trains. The first was a dark-panelled model used in the seasons where the show was filmed in black and white. The second was a more functional model decorated in green and gold. It's this train, which houses the unique gadgets associated with the show, that most people remember.
Ross Martin (Artemus Gordon) missed nine episodes due to a broken leg and a nearly fatal heart attack. He was not in season four, episodes ten, twelve, thirteen, fifteen, sixteen, seventeen, eighteen, twenty-one, and twenty-three.